JP4423696B2 - Heater control device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
  The present invention has a backlight.LCD display unitIn order to improve display brightness, extend the life of the backlight and save power in electronic devices equipped withHeater control deviceIt is about.
[0002]
[Prior art]
  Notebook personal computers and portable information terminals are often used outdoors because of their high portability, and therefore one issue is how to withstand the influence of environmental conditions (temperature, humidity, etc.).
[0003]
  As a display device for these devices, a liquid crystal display having a backlight using a fluorescent tube is often used. However, this backlight is easily affected by temperature and has a characteristic that the luminance is remarkably lowered at a low temperature.
[0004]
  In order to solve such a problem, a method of increasing the luminance by heating the backlight with a heater may be employed.
[0005]
  For example, a car speedometer with a backlightLCD display meterIn some cases, in order to ensure the brightness of the meter display, there is one having a function of heating the backlight with a heater for a certain period of time (about ten or more seconds) in the initial operation state before engine ignition. In this case, a heater having an output of several W to several tens of W is selected. The backlight whose temperature has increased due to the heating at the time of initial movement is ensured by the increase in ambient temperature by the air conditioner controlled by the driver after the heating is stopped.
[0006]
  Some vehicle-mounted liquid crystal televisions include a heater for heating the backlight.
[0007]
  Next, a heater control device for the above-described conventional liquid crystal display meter with a backlight of an automobile will be described with reference to FIG.
[0008]
  In FIG. 6, 21 is a backlight disposed at the rear of the liquid crystal display meter, 22 is an inverter for driving the backlight 21, 23 is a thermistor for measuring the temperature of the backlight 21, and 24 is for heating the backlight 21. A heater for driving the heater 24, a drive circuit for driving the heater 24, a key switch 26, a timer 27 for outputting a drive signal to the drive circuit 25 when the key switch is turned on and turning off the drive signal after a certain time , 28 are comparators for comparing the temperature detected by the thermistor 23 of the temperature detection circuit with the heating protection temperature, and 29 is a car battery.
[0009]
  In a state where the automobile engine is not started, the output S2 of the timer 27 is at a low level because the key switch 26 is off, and the drive circuit 25 is not operating, so the heater 24 is off.
[0010]
  Now, if the driver turns on the key switch 26 to start the engine,The timer 27 receives the signal S3 from the key switch 26 and starts counting internally, and the drive signal S2 becomes High level, and the drive circuit 25 operates to energize the heater 24. timerWhen the count value reaches a specified value (after ten seconds), the output S2 is set to a low level to turn off the output of the drive circuit 25 and turn off the heater 24. At this time, during heating by the heaterOf the backlight 21As a protective measure when the temperature rises abnormally, the comparator 28 detects the temperature detection signal from the thermistor 23.S1Is detected to exceed the specified value, the comparator 28Output S2 of timer 27Forcibly turns off the output of the drive circuit 25.The heating of the backlight 21 by the heater 24 is stopped.To work.
[0011]
[Problems to be solved by the invention]
  On the other hand, when a laptop computer, which is a portable electronic device, is used outdoors, it cannot be expected that the ambient temperature will increase due to the air conditioner like a car. To ensure the brightness of the backlight, It is necessary to keep the backlight temperature within a predetermined range by a heater for heating the backlight.
[0012]
  On the other hand, there are two main power sources for notebook computers: an AC adapter and a battery. Especially when battery operation is performed, if a large amount of power is allocated to the heater, the operation time of the main unit becomes extremely high.It will be shorter.
[0013]
  In addition, a notebook PC in a very low temperature requires a considerable amount of time to reach the brightness of the backlight at room temperature due to heater heating. The problem is whether a high backlight luminance can be ensured immediately after the start.
[0014]
  An object of the present invention is to solve the above-described conventional problems, maintain a backlight temperature in a predetermined range, reduce power consumption, and start a backlight with high brightness when an electronic device is started. It is to provide a control device.
[0015]
[Means for Solving the Problems]
  In order to solve this problem, the heater control device of the present invention has a power supply for an electronic device.Check that the AC adapter power supplyA detector to detect, a heater for heating the backlight, and power supply to the heaterON / OFFDetects the heater drive circuit and backlight temperatureTemperature detectorAnd a backlight on request signal output from the main body of the electronic deviceTemperature detectorIn order to keep the backlight temperature within a predetermined range according to the temperature signal fromHeater drive circuitHeater control means for controlling the backlight, a backlight on request signal,Temperature detectorBacklight control means for controlling on / off of the backlight in accordance with the temperature signal from is provided.
[0016]
  DetectorAC adapter power supplyIs detected regardless of the backlight on request signal linked with the display unit operation from the electronic device body,Temperature detectorHeater control means, heater drive circuit and heater control to control the power supply to the heater so as to keep the backlight temperature within a predetermined range, while the backlight responds to the backlight on request signalON / OFFTo be configured.
[0017]
  In this configuration, when the backlight on request signal is turned on from off, that is, when the electronic device is turned on or returned from a power saving mode such as standby, the backlight is already warmed to a predetermined temperature. A high-brightness backlight can be obtained at the same time as the device is started.
[0018]
  Also,If the battery power source is not detecting the AC adapter power source,When the backlight on request signal is on, the above-described heater control is performed. When the backlight on request signal is off, the heater is turned off, and the backlight responds to the backlight on request signal.ON / OFFTo be configured.
[0019]
  In this configuration, since the heater is controlled only during the operation of the display device of the electronic device, a power saving effect can be obtained.
[0020]
  Also,For battery power,When the backlight on request signal is turned on, the backlight is not turned on immediately, but the above-described heater control is started, and when the temperature of the backlight rises above a predetermined value, a preheating operation for turning on the backlight can be performed.
[0021]
  With this configuration, it is possible to prevent the backlight from being deteriorated or abnormally operated by turning on the low-temperature backlight.
[0022]
  Furthermore, the signal output from the heater control means to the heater drive circuit is a pulse with a variable duty (PWM signal), or the electric power supplied to the heater is more precisely controlled by selectively switching a plurality of heaters. It can be configured as follows.
[0023]
  According to this configuration, immediately after the backlight on request signal changes from off to on, the heater is heated rapidly by applying a large electric power to the heater or by generating heat from a plurality of heaters. By shortening the waiting time until the temperature reaches the predetermined temperature and reducing the power to the heater when the backlight temperature reaches a predetermined temperature, fine heater control and power saving can be achieved.
[0024]
  In addition, when the main body of the electronic device is on, the heater output can be precisely controlled in consideration of the self-heating of the backlight.
[0025]
DETAILED DESCRIPTION OF THE INVENTION
  The present invention is a heater control device for heating a backlight for display illumination of an electronic device operated by an AC adapter power source and a battery power source,The electronic device is poweredDetects AC adapter power supplyA detector, a heater for heating the backlight, and power supply to the heater;A heater drive circuit that turns on and off; andDetect the temperature of the backlightTemperature detectorAnd saidTemperature detectorHeater control means for controlling the drive circuit so as to maintain the temperature of the backlight within a predetermined range in accordance with the output of the backlight on request signal from the electronic device main body,When the detector is a battery power source that does not detect an AC adapter power source,The heater control means is configured to execute heater control by the heater control means if the backlight on request signal is backlight on, and to turn off the heater if the backlight on request signal is backlight off. The heater control deviceAC adapter power supplyIn this case, since the heater is always controlled regardless of the backlight on request signal according to the power off / standby of the electronic device, the operating state of the peripheral device and the power management, even when the electronic device starts operating, even in a low temperature environment A high-brightness backlight can be obtained.
[0026]
  Further, when the power source is a battery, the heater control is performed only during a period in which the display device is operating in the electronic device (a period during which the backlight on request signal is on), so that an effect of saving power and extending the battery life can be obtained.
[0027]
  The present invention also provides:A heater for heating the backlight and power to the heater;Heater drive circuit that turns on and offAnd detecting the temperature of the backlightTemperature detectorAnd saidDepending on temperature detector output and backlight on request signalIn order to keep the temperature of the backlight within a predetermined rangeHeater drive circuitHeater control means to control the power supply and power supply to the backlightON / OFFAnd a backlight control means for controlling the backlight drive circuit, and the detectorAC adapter power supplyIs detected, the backlight driving circuit is controlled according to the backlight on request signal to turn on the backlight.ON / OFFAndIf the power source is a battery,The backlight on request signal is on, andIf the backlight temperature detected by the temperature detector is equal to or lower than a predetermined temperature, the backlight is turned off, and the backlight temperature detected by the temperature detector is equal to or higher than a predetermined temperature. The backlight is heated by the heater untilWhen the temperature detector detects a predetermined temperature or higherThe power supply to the heater is turned off and the backlight is turned on.Since the backlight is turned on after the backlight is warmed to a predetermined temperature, it is possible to reliably turn on and extend the life of the backlight.
[0028]
  Further, the present invention comprises a heater switch that enables or disables heater control by the heater control means,When it is unnecessary even at low temperatures, the user can turn off the heater control and stop the heating by the heater, thereby reducing the power consumption of the electronic device.
[0029]
  Further, in the present invention, the heater drive circuit control by the heater control means is controlled by a PWM signal.When the backlight temperature is significantly lower than the target temperature, rapid heating is performed by maximizing the duty ratio, and when the backlight temperature reaches the target temperature, the heater ON / OFF duty ratioButThe backlight temperature can be kept within a predetermined range by controlling the value to be small.
[0030]
  The present invention also provides:A plurality of sets of the heater and the heater driving circuit;The heater control means can selectively turn on / off the power supply to multiple heaters.With this configuration, the maximum output can be obtained when the backlight temperature is significantly lower than the target temperature.pluralRapid heating by driving the heater,The waiting time until the backlight reaches the predetermined temperature is shortened,When the backlight temperature reaches the target temperature,By reducing the number of heaters driven so that the output is lowThe backlight temperature can be kept constant.
[0031]
  Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0032]
(Embodiment 1)
  FIG. 1 shows a configuration diagram of Embodiment 1 of the heater control apparatus of the present invention.
[0033]
  In FIG. 1, 1 is a main unit (electronic device body) of a personal computer, 2 is a liquid crystal display unit, 3 is a backlight built in the liquid crystal display unit 2, and 4 is a backlight drive for driving the backlight 3. An inverter which is a circuit, 5 is a thermistor which is a temperature detection circuit for measuring the temperature of the backlight 3, 6 is a heater for heating the backlight 3, and 7 is a heater driving circuit for turning on / off the power supply to the heater 6. , 8 is a microcontroller for controlling the heater drive circuit 7, and 9 is an on request signal for the backlight 3.S310 is an AC adapter that supplies power to the main unit 1, 11 is a battery that supplies power to the main unit 1 when the AC adapter 10 is not connected, and 12 and 13 are AC adapter 10 and the battery Reference numeral 14 denotes a diode for coupling the power supply from 11, and reference numeral 14 denotes a detector for detecting that power is supplied from the AC adapter 10.
[0034]
  The graphic controller 9 included in the main unit 1 outputs a backlight on request signal S3 for turning on / off the backlight together with the display according to an operation mode such as operation of the electronic device, power saving, and power off. This means may be provided in the heater control means of the present invention.
[0035]
  The detector 14 compares the input voltage or input current from the AC adapter 10 with a predetermined value, and outputs an AC adapter detection signal S2 indicating that the AC adapter is used as a power source if the input voltage or input current is equal to or greater than the predetermined value.
[0036]
  The microcontroller 8 receives the temperature detection signal S1 from the thermistor 5, the AC adapter detection signal S2 from the detector 14, and the backlight on request signal S3 from the graphic controller 9 which is a part of the display control circuit of the electronic device body. The control signal S4 is output to the heater drive circuit 7 and the control signal S5 is output to the inverter 4.
[0037]
  If power is supplied by the AC adapter, the heater control always operates unless the user turns off the heater with the switch 15 when the ambient temperature drops. However, depending on the environment in which the computer is installed, assuming an office, etc., the ambient temperature decreases in the time zone when the computer is not used, but the ambient temperature remains at room temperature in the time zone when the computer is used. There can be a situation where In this case, the constant operation of the heater during a time period when the computer is not used results in wasted power consumption.
[0038]
  In order to prevent this waste of electric power, since the switch 15 is provided for the heater control means by the microcontroller 8,When the user operates this switch, the heater is energized.Enable / disable can be selected and switched.
[0039]
  The operation of the heater control apparatus configured as described above will be described with reference to FIG.
[0040]
  FIG. 2 shows a heater control sequence in the first embodiment of the heater control apparatus of the present invention.
[0041]
  The microcontroller 8 has a heater inside.6It has a temperature table as a reference for turning on and off. As a temperature table,Energize the heater 6 and turn on the backlight 3Heater on temperature to start heating is Ton, heaterbyThe heater-off temperature at which heating is stopped is defined as Toff.
[0042]
  From thermistor 5Assuming that the temperature of the backlight 3 detected by the temperature detection signal S1 is TBL, TBL <TonSometimesMicrocontroller 8 is a control signalS4Is set to a high level to turn on the heater drive circuit 7, and when TBL> Toff, the microcontroller 8S4The heater drive circuit 7 is operated to be turned off by setting the signal to the low level.
[0043]
  In order to satisfy these conditions, the microcontroller 8 takes a control sequence as shown in FIG. Details of the control sequence will be described below.
[0044]
  [STEP1]
  The output signal S2 of the detector 14 indicates whether the power source is the AC adapter 10 or not.ByCheck. If it is an AC adapter, go to STEP2.PowerIf the battery 11 is not the AC adapter 10, the process proceeds to STEP 3.
[0045]
  [STEP2]
  The on / off state of the heater switch 15 is confirmed. If the heater switch 15 is off, proceed to STEP 8 to turn off the heater 6, and if the heater switch 15 is on, proceed to STEP 4 to control the heater.
[0046]
  [STEP3]
  When the power source is the battery 11, the power from the graphic controller 9 of the main body of the electronic deviceThe backlight on request signal S3 is confirmed. If there is a backlight on request, proceed to STEP 2; if there is no backlight on request, proceed to STEP 8.
[0047]
  [STEP4]
  Control signal S4 to heater drive circuit 7ByThe heater state of whether or not electric power is supplied to the heater 6 is confirmed.If the power supply to the heater 6 is off, go to STEP5, and if the power supply to the heater 6 is on, go to STEP7.
[0048]
  [STEP5]
  The temperature (TBL) of the backlight 3 detected by the temperature detection signal S 1 from the thermistor 5 is compared with the heater on temperature (Ton) of the temperature table by the microcontroller 8.TBL <TonIfReturn to STEP6. If TBL ≧ Ton, return to STEP1.
[0049]
  [STEP6]
  If TBL <Ton in STEP 5, the heater driving circuit 7 is turned on by the control signal S4, the power is supplied to the heater 6, and the backlight 3 is heated. And the sequence isReturn to STEP1.
[0050]
  [STEP7]
  If the power supply to the heater 6 is on in step 4, the temperature (TBL) of the backlight 3 is compared with the heater off temperature (Toff) by the microcontroller 8.If TBL> Toff, return to STEP8, and if TBL ≦ Toff, return to STEP1.
[0051]
  [STEP8]
  From microcontroller 8The control signal S4 becomes Low levelThe heater drive circuit 7 is turned off, the power supply to the heater 6 is turned off, and the heating of the backlight 3 is stopped..
[0052]
  STEP4 to STEP8 are backlights3Step 9 of the heater control for maintaining the temperature in the predetermined range is configured.
[0053]
  The heater switch 15 controls the heater to increase the luminance of the backlight 6 or is controlled by the heater 6.Backlight 6This is for the user to select whether to stop heating and save power. If this selection is unnecessary, it can be omitted.
[0054]
  The operations and effects of the heater and the backlight according to this control sequence are as follows.
[0055]
  When the AC adapter is used as the power source, the heater control is always operated, the backlight temperature is kept within a predetermined range, and the brightness of the back-lit liquid crystal display can be secured even immediately after the computer main body is started. In addition, when the battery is used as a power source, the heater control operates only when the liquid crystal display is performed in accordance with the backlight on signal from the electronic device, so that power can be saved.
[0056]
  (Embodiment 2)
  Next, a second embodiment of the heater control device of the present invention will be described with reference to FIGS.
[0057]
  FIG. 3 shows a control sequence of the heater control apparatus according to the second embodiment of the present invention.
[0058]
  If the backlight is turned on when the backlight temperature is low, the backlight may not turn on or may turn on abnormally, which may shorten the life of the backlight. When the light is turned on, it is desirable that the temperature be higher than a certain level.
Embodiment 2 isWhen the backlight is off and the temperature is low, preheating is performed before turning on the backlight so that the backlight temperature is raised to a predetermined value and the backlight is turned on.WhatThis will be described below with reference to FIGS.
[0059]
  In the second embodiment, the hardware configuration is the same as in FIG. 1, and the microcontroller 8 executes the following control sequence.
[0060]
  [STEP 11]
  The output signal S2 of the detector 14 indicates whether the power source is the AC adapter 10 or not.ByCheck. If it is AC adapter 10, go to STEP12.PowerIf the battery 11 is not the AC adapter 10, the process proceeds to STEP 13.
[0061]
  [STEP 12]
  From graphic controller 9The backlight on request signal S3 is confirmed. If there is a backlight on request, proceed to STEP 16, and if there is no backlight on request, proceed to STEP 15.
[0062]
  [STEP 13]
  On the other hand, even when the power source is the battery 11, the graphic controller 9The backlight on request signal S3 is confirmed. If there is a backlight on request, the process returns to STEP 14, and if there is no backlight on request, the process returns to STEP 11.
[0063]
  [STEP14]
  According to the temperature detection signal S1 from the thermistor 5The backlight temperature (TBL) is compared with the heater on temperature (Ton). If TBL <Ton, go to STEP15, and if TBL ≧ Ton, go to STEP16.
[0064]
  [STEP 15]
  Microcontroller 8Backlight3The control signal S5 for turning off is output, and the process proceeds to STEP17.
[0065]
  [STEP 16]
  Microcontroller 8Backlight3The control signal S5 for turning on is output, and the process proceeds to STEP17.
[0066]
  [STEP 17]
  The heater control, which is a processing procedure equivalent to STEP 9 configured in STEP 4 to STEP 8 in FIG. 2, returns to STEP 11 after processing.
[0067]
  (Embodiment 3)
  Next, Embodiment 3 of the present invention will be described with reference to FIG.
[0068]
  FIG. 4 shows a block diagram of a third embodiment of the heater control device of the present invention.
[0069]
  Embodiment 3InThe microcontroller 81 outputs the control signal S4 to the heater drive circuit 7 as a PWM signal whose duty ratio changes in STEP6 of FIG.Power supplyThe microcontroller 81 controls theThe temperature of the backlight 3 detected by the temperature detection signal S1 from the thermistor 5The difference from the first embodiment is that the control signal S4 is output as a PWM signal according to the above.
[0070]
  For example, the resistance value of the heater 6 = 10Ω, the heater6When the supply voltage Vo is 15 V, the output power of the heater 6 is 22.5 W.
[0071]
  On the other hand, the control signal S4 is output as a PWM signal by the microcontroller 81, and its duty ratio is, for example, 1/3, 2/3,Heater 6The output power is 7.5 W and 15.0 W.
[0072]
  The duty ratio of the PWM signal is detected by the thermistor 5.Of backlight 3Varies with temperature. That is, when the temperature of the backlight 3 is low, the microcontroller 81 maximizes the output of the heater by setting the control signal S4 to a high level, and when the temperature of the backlight 3 rises, the microcontroller 81 determines the duty ratio of the control signal S4. The backlight temperature is controlled to be constant by changing the heater and adjusting the heater output.
[0073]
  (Embodiment 4)
  Next, a fourth embodiment of the heater control device of the present invention will be described with reference to FIG.
[0074]
  FIG. 5 is a configuration diagram of a heater control circuit that switches the heater output by switching the connection state of a plurality of heaters, and includes a plurality of heaters 6, 6 ′, 6 ″ and heater drive circuits 7, 7 ′, 7 ″. This is the difference from the first embodiment.
[0075]
  For example, the resistance value of the heaters 6, 6 ′, 6 ″ is 30Ω, and the supply voltage Vo to the heaters 6, 6 ′, 6 ″ is 15 V.
[0076]
  When only the heater drive circuit 7 is on, the output power of the heater is 7.5W. On the other hand, when the heater driving circuit 7 'is turned on, the heater output power is 15.0 W, and when all the heater driving circuits 7, 7', 7 "are turned on, the heater output power is 22.5 W.
[0077]
  Which heater drive circuit is operated varies according to the temperature of the backlight 3 detected by the thermistor 5. That is, when the temperature of the backlight 3 is low, the microcontroller 82 maximizes the output of the heater by maximizing the number of heater driving circuits to be operated.Than the temperatureWhen it rises, the microcontroller 82 controls the backlight temperature to be constant by decreasing the number of heater drive circuits to be turned on and adjusting the heater output.
[0078]
  Although the embodiment for controlling the number of heaters has been described, the magnitude of the heater wattage may be controlled. When the difference between the backlight temperature and the predetermined temperature is large, a heater with a large wattage is driven. When the temperature reaches a predetermined temperature, a heater with a small wattage is driven.AlsoSimilar effects can be obtained.
[0079]
  The present invention is not limited to the above-described embodiment, and FIGS. 2 to 5 may be combined.
[0080]
【The invention's effect】
  As described above, according to the present invention, when an electronic device is used with a battery as a power source in a low temperature environment, the backlight is automatically turned off and heated by the heater, and the temperature of the backlight is set. When the temperature exceeds the specified temperature, heating by the heater is stopped and the backlight is turned on, so that when the electronic device is started up in this low temperature environment, it goes through a preheating operation that heats the backlight without turning on the backlight. Therefore, the backlight can be activated with high brightness, and the backlight is turned off during preheating. Therefore, power consumption is reduced, and at the same time deterioration caused by operating the backlight at a low temperature. It can be prevented.
In addition, by providing a heater switch that stops the power supply to the heater by the heater drive circuit,Even when the backlight on request signal generating means generates a backlight on request signal, it prevents power supply to the heater and reduces power consumption.It is effective that it can save power.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of first and second embodiments of a heater control device of the present invention.
FIG. 2 is a heater control sequence diagram of the first embodiment of the heater control device of the present invention.
FIG. 3 is a heater control sequence diagram of the second embodiment of the heater control device of the present invention.
FIG. 4 is a configuration diagram of a third embodiment of a heater control device according to the present invention.
FIG. 5 is a configuration diagram of a fourth embodiment of a heater control device according to the present invention.
FIG. 6 is a configuration diagram of a conventional heater control device.
[Explanation of symbols]
  1 Main unit
  2 Liquid crystal display unit
  3 Backlight
  4 Inverter
  5 Thermistor
  6 Heater
  7 Heater drive circuit
  8, 81, 82 Microcontroller
  9 Graphic controller
  10 AC adapter
  11 batteries
  12 diodes
  13 Diode
  14 Detector
  15 switch

Claims (3)

A heater control device for heating a backlight for display illumination of an electronic device operated by an AC adapter power source and a battery power source,
A detector for detecting the AC adapter power supply; a heater for heating the backlight; a heater driving circuit for turning on / off power supply to the heater; a temperature detector for detecting a temperature of the backlight; Heater control means for controlling the heater drive circuit so as to maintain the temperature of the backlight in a predetermined range according to the output of the temperature detector, a backlight drive circuit for supplying power to the backlight, and the backlight Backlight control means for controlling the drive circuit, backlight on request signal generation means for generating a signal for requesting the backlight to be turned on, and the heater control means stop supplying power to the heater by the heater drive circuit Has a heater switch,
When the detector detects an AC adapter power supply in a state where power supply to the heater is not stopped by the heater switch, backlight control is performed by a backlight on request signal from the backlight on request signal generating means. When the means controls the backlight driving circuit and power is supplied to the backlight to turn on the backlight, and the detector uses a battery that does not detect the AC adapter power supply as a power source, the backlight on request signal is If the backlight temperature detected by the temperature detector is equal to or lower than a predetermined temperature, the backlight control means stops supplying power to the backlight by the backlight driving circuit. The heater control circuit supplies power to the heater by the heater control means to When the temperature detector detects that the temperature of the backlight is equal to or higher than a predetermined temperature due to heating of the backlight by the heater, the heater control means uses the heater drive circuit to The power supply to the heater is stopped, and the backlight drive circuit supplies power to the backlight by the backlight control means to turn on the backlight,
When the heater control means stops the power supply to the heater by the heater drive circuit by the heater switch, even if a backlight on request signal is generated from the backlight on request signal generating means, A heater control device characterized in that the power supply is blocked .   2. The heater control apparatus according to claim 1, wherein the control of the heater drive circuit by the heater control means is a PWM signal.   The heater includes a plurality of heaters, and the heater drive circuit includes a plurality of heater drive circuits for turning on and off power supply to the plurality of heaters, and a backlight temperature detected by the temperature detector is low. Then, the heater control means controls the plurality of heater driving circuits so as to maximize the number of heaters that supply power, and the backlight temperature detected by the temperature detector is controlled by the plurality of heater driving circuits. When the heater reaches a predetermined temperature higher than the maximum temperature at which the number of heaters to be supplied reaches, the heater control means controls the plurality of heater drive circuits so as to reduce the number of heaters to be supplied with power from the maximum number. The heater control device according to claim 1, wherein the heater control device is configured.

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